The present invention relates to a multi-passage swivel joint for the separate and simultaneous tranfer of a plurality of pressure fluids between two groups of corresponding conduits, the second group rotating about the first one.
Such a joint allows, for instance, the transfer of several different fluids under possibly different pressures between two elements of a machine subjected to relative rotation. It is particularly suited to the transfer of fluids between a marine structure used for offshore oil production from subsea wellheads and a floating facility intended for the storage and treatment of this production, such application by no means being restrictive.
The marine structure can be a mooring buoy anchored at a distance from shore. It can also be a tower or articulated column anchored on the seabed. The floating facility is usually a storage vessel or a floating plant.
The production of oil from subsea wells requires that several different fluids, for instance crude oil or gas, water, drilling mud, oil for hydrostatic systems etc . . . be simultaneously transferred between the floating facility and the marine structure which is connected to subsea wellheads by flexible or rigid pipes.
The floating facility subjected to wind, wave and current action must be able to weathervane around the marine structure to which it is moored.
To maintain the segregation of the various fluids to be tranferred during weathervaning, it is necessary to install a multi-passage swivel joint at the floating facility mooring point on the marine structure.
The pipes channeling the various fluids to this swivel unit can be arranged in two groups of coaxial conduits, corresponding to one another and rotatable relative to each other. They can also be arranged parallel to each other in bundles or arranged radially around the axis of rotation of the floating facility about the marine structure.
Multi-passage swivel units are already in use for the separate and simultaneous transfer of a plurality of pressure fluids between two groups of concentric conduits arranged in bundles or radially, mainly for fluid transfer between a fixed marine structure and a floating facility weathervaning around the marine structure. With such arrangements, segregation continuity during rotation is maintained by the mere sliding of the seals on their bearing area. But the statistically most frequent relative displacements, imposed to these components due to the action of sea elements on the floating facility, are small alternating angular motions usually less than .+-.10.degree..
The frequent reversals in direction of the friction torque applied on these seals make it difficult to mechanically design reliable and fatigue resistant joints. Moreover, these small motions which account for 90% of all motions cause rapid wear of the seals.
The prior art may be illustrated by the following U.S. Pat. Nos. 4,250,918; 4,183,559 and 4,099,542.